This invention relates to multilamp photoflash units and, more particularly, to a high voltage photoflash unit construction with improved means for economically securing components and providing electrostatic protection.
Numerous multilamp arrangements with various types of sequencing circuits have been described in the prior art, particularly in the past few years. A currently marketed photoflash unit (described in U.S. Pat. Nos. 3,894,226 and 4,017,728 and referred to as flipflash) employs high voltage type lamps adapted to be ignited sequentially by successively applied high voltage firing pulses from a source such as a camera-shutter-actuated piezoelectric element. The flipflash unit comprises an elongated planar array of eight high-voltage type flashlamps mounted on a printed circuit board with an array of respectively associated reflectors disposed therebetween. The lamps are arranged in two groups of four disposed on the upper and lower halves respectively of the rectangular-shaped circuit board. A set of terminal contacts at the lower end of the unit is provided for activation of the upper group of lamps, while a set of terminal contacts at the top of the unit is operatively associated with the lower group of lamps. The application of successive high voltage pulses (e.g. 2000 to 4000 volts from, say, a piezoelectric source controlled by the shutter of a camera in which the array is inserted) to the terminal contact at the lower end of the unit causes the four lamps at the upper half of the array to be sequentially ignited. The array may then be turned end for end and again inserted into the camera in order to flash the remaining four lamps. In this manner one group of lamps (or half of the array) functions as a flash extender for the other group of lamps so that only the group of lamps relatively farther from the camera lens axis may be flashed. The purpose of such an arrangement is to position the active group of flashlamps farther above the camera lens in order to reduce the possibility of a "red-eye" effect that causes the pupils of a person's eyes to appear red or pink in flash pictures taken when the flashlamp is close to a camera lens.
In order to provide electrostatic shielding for the lamps and circuitry, the reflector member is rendered electrically conductive by a reflective metalized coating thereon, and this coating is electrically connected to a common circuit conductor run on the printed circuit board. Further, a metal foil is laminated on the indicia sheet and also connected to this common conductor run of the circuit board.
A copending patent application Ser. No. 072,251, assigned to the present assignee, describes a more compact, cost-efficient photoflash unit construction comprising a linear array of electrically ignitable flashlamps mounted on a printed circuit board in the form of an elongated strip. The printed circuit strip is located within the longitudinal channel of an elongated housing member having a continuous coating of conductive-reflective material thereon adjacent to the lamps. A light-transmitting cover panel is attached to the front of the housing member to enclose the flashlamps. The lamps have substantially tubular envelopes and are positioned extremely close to one another with their longitudinal axes substantially parallel to the surface of the printed circuit strip and in substantially coaxial alignment. Typically, the diameter of the lamps, the width of the printed circuit strip, and the width of the channel in the housing member are nearly equal. In order to provide protection against the red-eye effect, a double-ended linear array is described which operates in similar fashion to the aforementioned flipflash. In one specific embodiment, three lamps mounted in the upper half of the printed circuit strip are controlled by a pair of contact terminals at the lower end of the unit, while three lamps in the lower half of the unit are controlled by contact terminals at the top end of the unit. One of the contact terminals for controlling a group of lamps is connected in common to a lead-in wire of each of the lamps of the group, while the other contact is a "hot", or signal, terminal coupled through switching circuitry to the other lead-in wire of each of the lamps. Accordingly, in order to provide an interconnection between the signal terminals at each end of the unit and the respective switching circuitry controlled thereby on opposite halves of the printed circuit strip, respective signal conductor runs must be extended through the respectively inactive halves of the circuit strip. The interconnecting conductor runs from the common terminal contacts are disposed along the outer sides of the circuit-containing surface of the printed circuit board. More specifically, the common circuit conductor run on the bottom half of the circuit strip is located on the opposite side of the circuit board surface from the common circuit run on the top half of the circuit strip. As a result, a crossover, or side-to-side connection of the common circuit run is required in order to connect the common terminal at one end of the printed circuit strip with the common circuit conductor run connected to lamp leads in the opposite half of the circuit strip. Such a problem is created by the severe crowding of the conductive paths of this extremely compact unit. The use of printed conductor runs on both sides of the circuit strip with conventional through-connections introduces undesirable cost, e.g. two circuit screening operations are needed together with eyelets, plated-through holes, or the like. A minimum inter-run spacing of about 1.5 millimeters is necessary in order to prevent failure, i.e. promoting electrical sparkover from one run to another at the high voltages used (e.g., 2000 volts or more).
A copending patent application Ser. No. 084,236, filed concurrently herewith and assigned to the present assignee, overcomes the aforementioned problem of interconnecting the spaced common circuit runs by attaching a staple to the printed circuit board. The center region of the staple is positioned on the opposite side of the circuit board from the surface carrying the conductor runs, and the two legs of the staple extend through the circuit board and are bent over the conductor-carrying surface in contact with respective common circuit runs, thereby providing a jumper therebetween. Upon placing the circuit board in the housing channel, the center region of the staple is disposed between the circuit strip and channel wall in contact with the conductive-reflective coating. In this manner the conductive wall coating is grounded to common to provide an electrostatic shield for the unit.
Protection against electrostatic charges about the front face of the unit described in the above-referenced copending application Ser. Nos. 072,251 and 084,236, is provided in a manner following the teachings of U.S. Pat. No. 4,133,424. More specifically, the light-transmitting cover panel is provided with a plurality of openings, and conductive projections from the housing member, protrude through the cover openings to extend the circuit ground to the exterior of the front face of the unit. The aforementioned constructions, however, do not provide such an exterior ground mode of protection for the rear of the unit.
Further yet, the comparatively simplified linear array structure described in the aforementioned copending applications has an open channel within which the strip-like printed circuit board is located. Accordingly, some means must be provided for securing the printed circuit strip within the housing channel. In the above-referenced application Ser. No. 072,251, location and centering of the circuit strip within the channel is provided by guide ribs, molded in opposite sidewalls of the channel, which engage notches provided in opposite edges of the circuit strip. In Ser. No. 084,236, the circuit strip is described as being secured to the channel by means such as providing an interference fit with the channel sidewalls or by applying a cement between the back of the strip 18 and the rear wall of the channel.